Place the radicchio and onion in a bowl, season with salt and pepper, and drizzle over the orange juice and olive oil. Toss well, and let sit for 10 to 20 minutes.
Roll out the flatbread or pizza dough onto a rimmed baking sheet. Toss the radicchio and onion again, and distribute the vegetables over the flatbread, spreading them evenly in a thin layer almost to the edges. Sprinkle over the thyme. Bake for 12 minutes, then sprinkle the blue cheese over the vegetables and bake for another 3 to 6 minutes until the dough is cooked through and fairly firm, and the blue cheese has started to melt.
Drizzle the honey over the pizza in a thin stream. Cut the flatbread in half lengthwise, then cut the flatbread crosswise into 8 segments, resulting in 16 rectangular strips. Dollop the pieces with the Whipped Ricotta, if using. Serve hot or warm.